Thursday, January 29, 2009

A Winter Surprise

A very interesting morning to say the least across parts of East Texas this morning; snow. Yes, in areas that saw the thickest fog we did see a little light snowfall this morning from a rare atmospheric setup we normally do not see around here. So what happened? In the lowest levels of the atmosphere this morning, between 1000’ and 1500’, there was a little lift indicated, a small area of instability causing the air to rise in this level. Now the amount of energy available was not enough to cause widespread precipitation this morning by itself. Just above this layer temperatures were warming to near 50°F and this caused the air above the fog to begin lifting as well. When you combine the two there was just enough lift to cause light precipitation to form. This happens a lot in the warmer months, right before dense fog lifts, when sometimes you will notice a heavy mist beginning to fall. Since temperatures were in the middle 20s, the water vapor in the atmosphere began to crystallize forming snow grains. Now in order to get a true snow flake to form the temperature needs to be around 14°F to get a branching crystal growth, or what we call in the meteorological world dentritic crystal growth. But it was cold enough to have what we call hexagonal crystal growth where small, needle like snow grains form. These snow grains then continue to grow in the moist fog layer until they are heavy enough to fall to the surface. So where the fog was thickest, we saw enough moisture available for this light snow to grow and fall to the surface. Here are a few photos sent to me from the Longview Kilgore area where most of this winter phenomenon occurred.

So a very fun surprise for most across East Texas who were expecting a little ice yesterday and got a light snow today. This happens many times in areas of the world were you see thick fog and cold air together but around here, well I guess there is a first time for everything.

1 comment:

Jeff said...

Best weather blog ever.